Rotary drag bit with increased back rake angle gauge cutter

ABSTRACT

A fixed cutter rotary drill bit having gauge cutting elements at large back rake angles are disclosed. The gauge is located at the outer diameter side wall portion of the bit that extends from the cutting end. The gauge and its cutting components contact the side wall of the bore hole during drilling operations. The gauge cutting elements may be configured at a back rake angle in a range of about 40° to 70°.

This application claims priority to and the benefit of U.S. Provisional Patent Application No. 60/889,403, which was filed on Feb. 12, 2007, incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in general to rotary drag bits and, in particular, to an improved system, method, and apparatus for a rotary drag bit having gauge cutting elements configured at large back rake angles.

2. Description of the Related Art

Earth-boring bits of the fixed cutter variety, commonly referred to as drag bits, have no moving parts and employ an array of hard inserts to scrape and shear formation material as the bit is rotated in the borehole. Inserts on prior art fixed cutter bits are typically aligned such that the inserts scrape the material from the borehole bottom. For scraping to take place, the longitudinal axis of the insert is typically at a small acute angle (e.g., 0° to 30°) relative to the bit face. Such an alignment places the cutting face of a cylindrically-shaped insert nearly perpendicular to the borehole bottom. The contact area between the cutting element and the formation starts out very small but increases rapidly as penetration or depth of cut becomes deeper.

High impact side-loading of drill bits during operation results in non-compressive loading of the interface between the diamond and tungsten carbide components on PDC cutters. This leads to broken and/or chipped cutters in the upper shoulder and gauge areas of the bit profile. High residual stresses are inherent in this interface area as a result of varying planar and non-planar geometries and the cutter manufacturing process. An improved solution that overcomes these problems would be desirable.

SUMMARY OF THE INVENTION

Embodiments of a system, method, and apparatus for a fixed cutter rotary drill bit having gauge cutting elements at large back rake angles are disclosed. The gauge is located at the outer diameter side wall portion of the bit that extends from the cutting end. The gauge and its cutting components contact the side wall of the bore hole during drilling operations.

In accordance with the invention, the gauge cutting elements may be configured at a back rake angle in a range of about 40° to 70°. For applications where cutter damage is a concern and side-cutting aggressiveness is a low priority, a very high back rake angle helps ensure compressive cutter loading when side impact forces are higher.

The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.

FIG. 1 is an isometric view of one embodiment of drill bit constructed in accordance with the present invention;

FIG. 2 is a schematic representation of half of a cutting profile of the drill bit of FIG. 1 and is constructed in accordance with the present invention;

FIG. 3 is an illustration of cutter element manipulation;

FIG. 4 is a side view of a cutting element showing a conventional back rake angle;

FIG. 5 is a side view of one embodiment of a cutting element showing a back rake angle constructed in accordance with the present invention; and

FIG. 6 is a side view of another embodiment of a cutting element showing a back rake angle constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, one embodiment of a fixed cutter rotary drill bit 11 is shown. Bit 11 has a bit axis 12 and a threaded end 13 for connection into a drill string. A cutting end 15 at a generally opposite end of the bit 11 is provided with a plurality of hard cutting elements 17 (e.g., polycrystalline diamond cutters, etc.) arranged about cutting end 15 to effect efficient disintegration of formation material as bit 11 is rotated in a bore hole.

As shown in the embodiment of FIG. 5, each cutting element 17 has a cylindrical base 19 with an axis 20, and is secured in a preformed pocket 21 provided on cutting end 15 and a cutting face 23 that engages the formation material. As illustrated, cutting element 17 may comprise a frustoconical cutting end that forms a beveled edge adjacent the face 23. Cutting element 17 acts somewhat like a plow that generally directs a high percentage of the material of the formation up its flat face.

Referring now to FIGS. 1 and 2, the arrangement of cutting elements 17 on bit 11 is configured in an overall cutting profile 25 (approximately half of which is shown in FIG. 2) about bit axis 12. Starting at axis 12 at the inner diameter of bit 11 and moving toward the outer diameter of bit 11 (right to left in FIG. 2), profile 25 comprises various areas, including a cone 27, a nose 29, a shoulder 31, and a gauge or gauge pad or surface 33. The gauge 33 is on a radially outermost portion of the bit body relative to the bit axis 12.

The gauge 33 essentially defines the flat, outer diameter side wall portion of bit 11 that extends from cutting end 15 (FIG. 1). The gauge 33 and its cutting components are proximal to and contact the side wall 34 (see FIG. 3) of the bore hole during drilling operations with bit 11. As shown in FIG. 1, a plurality of channels or grooves 35 (e.g., junk slots) extend from cutting end 15 through gauge 33 to provide a clearance area for the removal of cuttings and chips formed by cutting elements 17.

As shown in FIG. 1, a plurality of cutting elements 17 are provided on gauge 33 of bit 11. Active, gauge cutting elements 17 on gauge 33 provide the ability to actively cut formation material at the side wall 34 (FIG. 3) of the bore hole to provide dynamic stability and improved gauge-holding ability in earth-boring bits of the fixed cutter variety. As FIG. 1 illustrates, at least some of the gauge cutting elements 17 on gauge 33 may be ground flat at the outer diameter of bit 11 for some types of applications. Bit 11 is illustrated as a polycrystalline diamond cutter (PDC) bit, but cutting elements 17 are equally useful in other fixed cutter or drag bits that include a gauge or gauge surface for engagement with the side wall of the bore hole. Examples include impregnated and natural diamond bit cutting elements.

Referring now to FIG. 4, one type of prior art cutting element 117 for cutting formation is shown. Cutting element 117 is a conventional PDC cutting element and is cylindrical in shape. Cutting element 117 has an axis 120 and a diamond table on its face 123 with an essentially circular cross-section. Cutting element 117 has a cutter back rake angle 140 of 20°. However, conventional cutter back rake angles of 5° to 30° also are known.

As shown in FIG. 3, the circle 23 represents the face of cutting element 17 on the gauge 33. A back rake axis 42 is shown as vertical in the drawing, and parallel to the gauge 33, bit axis 12, and the bore side wall 34. A side rake axis 44 is perpendicular to axis 42, gauge 33, the bit axis 12, and the bore side wall 34.

In a “nominal” position on the gauge 33, both the back rake angle and the side rake angle of element 17 are zero. Thus, in one embodiment of the nominal position, face 23 extends in the plane defined by axes 42, 44, such that it is perpendicular to the gauge 33 and bore sidewall, and face 23 is parallel to axes 12, 42 and 44. Rotating the face 23 about axis 42 results in a modification to the back rake angle. In the gauge area 33, a positive back rake angle inclines the cutting face 23 away from the bit axis 12 and toward the borehole 34. Rotating the face 23 about axis 44 results in a modification to the side rake angle. A positive side rake angle includes the cutting face 23 away from the drill string and toward the bottom of the bore hole.

Referring again to FIG. 5, one embodiment of cutting element 17 in accordance with the invention is shown with a relatively large positive back rake angle 42 of 40°, and a 0° side rake angle. In FIG. 6, another embodiment of cutting element 17 is shown at a 65° back rake angle 42, and a 0° side rake angle. The invention may comprise back rake angles of approximately 40° to 70°.

For applications where cutter damage is a concern and side-cutting (e.g., cutting with the gauge 33 of the cutting profile 25) aggressiveness is a low priority, a very high back rake angle help ensures compressive cutter loading when side impact forces are higher. This is accomplished by lowering the y-component force (see, e.g., FIGS. 5 and 6) that results from side loads.

For example, comparing FIGS. 4 and 5, lower back rake angles result in higher loading in the y-direction, as depicted by the vectors F_(y). This is detrimental to cutter integrity with respect to the diamond/tungsten carbide interface where residual stresses are high. Although the direction of overall force, F_(f) (which is normal to the bore side wall 34), will vary slightly with dynamic events, the invention enhances the cutter integrity and dynamic stability of fixed cutter drill bits.

While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. 

1. A fixed cutter rotary drill bit, comprising: a bit body having a bit axis and a cutting profile defined about the bit axis, the cutting profile including a cone extending from the bit axis, a nose adjacent the cone, a shoulder adjacent the nose, and a gauge adjacent the shoulder, the gauge being adapted to engage a side wall of a bore hole during drilling operations; and a plurality of cutting elements extending from the cone, nose, shoulder and gauge of the cutting profile, and at least one of the cutting elements extending from the gauge has a back rake angle in a range of 40° to 70°.
 2. The fixed cutter rotary drill bit of claim 1, wherein the cutting elements are selected from the group consisting of polycrystalline diamond cutters (PDC), and impregnated and natural diamond bit cutting elements.
 3. The fixed cutter rotary drill bit of claim 1, wherein at least some of the cutting elements extending from the gauge are ground flat at an outer diameter of the bit body.
 4. The fixed cutter rotary drill bit of claim 1, wherein each cutting element has a cylindrical base that is secured in a pocket in the bit body, a cutting element axis, and a cutting face with a beveled edge.
 5. The fixed cutter rotary drill bit of claim 4, wherein the cutting face extends in a plane defining a back rake axis and a side rake axis that is perpendicular to the back rake axis, with both the back rake and side rake axes extending through the cutting element axis, and the back rake axis being parallel to a surface of the gauge and the bit axis, such that a positive back rake angle at the gauge inclines the cutting face away from the bit axis.
 6. The fixed cutter rotary drill bit of claim 5, wherein the back rake angle is 40°.
 7. The fixed cutter rotary drill bit of claim 5, wherein the back rake angle is 65°.
 8. A fixed cutter rotary drill bit, comprising: a bit body having a bit axis, a threaded end for connection into a drill string, a cutting end opposite the threaded end, and a cutting profile defined about the bit axis, the cutting profile including a cone extending from the bit axis, a nose adjacent the cone, a shoulder adjacent the nose, and a gauge adjacent the shoulder and on a radially outermost portion of the bit body relative to the bit axis, the gauge being adapted to engage a side wall of a bore hole during drilling operations; and a plurality of cutting elements extending from the cutting end in the cone, nose, shoulder and gauge of the cutting profile, and at least one of the cutting elements extending from the gauge has a back rake angle in a range of 40° to 70°.
 9. The fixed cutter rotary drill bit of claim 8, wherein the cutting elements are selected from the group consisting of polycrystalline diamond cutters (PDC), and impregnated and natural diamond bit cutting elements.
 10. The fixed cutter rotary drill bit of claim 8, wherein at least some of the cutting elements extending from the gauge are ground flat at an outer diameter of the bit body.
 11. The fixed cutter rotary drill bit of claim 8, wherein each cutting element has a cylindrical base that is secured in a pocket in the cutting end, a cutting element axis, and a cutting face with a beveled edge.
 12. The fixed cutter rotary drill bit of claim 11, wherein the cutting face extends in a plane defining a back rake axis and a side rake axis that is perpendicular to the back rake axis, with both the back rake and side rake axes extending through the cutting element axis, and the back rake axis being parallel to a surface of the gauge and the bit axis, such that a positive back rake angle at the gauge inclines the cutting face away from the bit axis.
 13. The fixed cutter rotary drill bit of claim 12, wherein the back rake angle is 40°.
 14. The fixed cutter rotary drill bit of claim 12, wherein the back rake angle is 65°.
 15. A fixed cutter rotary drill bit, comprising: a bit body having a bit axis, a threaded end for connection into a drill string, a cutting end opposite the threaded end, and a cutting profile defined about the bit axis, the cutting profile including a cone extending from the bit axis, a nose adjacent the cone, a shoulder adjacent the nose, and a gauge adjacent the shoulder and on a radially outermost portion of the bit body relative to the bit axis, the gauge being adapted to engage a side wall of a bore hole during drilling operations; a plurality of cutting elements extending from the cutting end in the cone, nose, shoulder and gauge of the cutting profile, each cutting element having a cylindrical base, a cutting element axis, and a cutting face, wherein the cutting face extends in a plane defining a back rake axis and a side rake axis that is perpendicular to the back rake axis, with both the back rake and side rake axes extending through the cutting element axis, and the back rake axis being parallel to a surface of the gauge and the bit axis, such that a positive back rake angle at the gauge inclines the cutting face away from the bit axis; and at least one of the cutting elements extending from the gauge has a back rake angle in a range of 40° to 70°.
 16. A fixed cutter rotary drill bit according to claim 15, wherein the cutting elements are selected from the group consisting of polycrystalline diamond cutters (PDC), impregnated and natural diamond bit cutting elements.
 17. A fixed cutter rotary drill bit according to claim 15, wherein at least some of the cutting elements extending from the gauge are ground flat at an outer diameter of the bit body.
 18. A fixed cutter rotary drill bit according to claim 15, wherein the back rake angle is 40°.
 19. A fixed cutter rotary drill bit according to claim 15, wherein the back rake angle is 65°. 